Syncing issue between Google Calendar and Calendar app in MacBook Pro

I've had this problem for years and every so often I go back to it to try and sort it and end up getting so fed up and stressed.

I uses iCal in Mac Book Pro - have more than one calendar for each thing i.e. a calendar for appointments, a calendar for birthdays, a calendar for my work schedule.

I have added/synced these via Google Calendar so they appear on my phone via Google calendar or the Samsung calendar.

When I add events/appointment on my Mac Book in iCal, they sync just fine with my phone.

However, I can't add appointments/events on my phone, so they appear on my Mac Book, like at all, it just doesn't give me the option to select whatever calendar I need. And I don't understand why, like surely that's one of the main reasons you would want to sync you calendars between devices.

It's really upsetting me because I have lots of appointments and things to remember, but I keep forgetting them because I can't add them in my phone.

PLEASE can someone help me with this, its really doing my head in.

Thank you!

[Re-Titled by Moderator]

Original Title: Ical/Google Cal syncing issues